This invention relates generally to window lifts or regulators, and more particularly to guiderails for the same and an apparatus and method for their manufacture.
Automotive vehicles have movable windows that may be opened and closed via window lift or regulator assemblies that are often supplied as modules for assembly to the door. These assemblies may be either manually operated or power controlled. Such regulator assemblies can have tape drive or cable drive mechanisms, each having many similar components.
For example, a conventional moveable window glass of an automotive door is slidably supported at its front and back ends by guides. The window glass is raised and lowered by a window regulator that fixed to the door and includes a bracket assembly that is secured to the lower end of the window glass. The bracket assembly runs on a vertical guiderail that is supported by and housed within the automotive door and that frequently includes a guide channel or rail that includes the surface over which the bracket moves and with which the bracket is in contact during operation of the regulator assembly. The bracket assembly is moved vertically on the guiderail by a flexible multistrand cable, mechanical arms, rack and pinion or planetary mechanisms or flexible tape. The ends of the cable or tape are attached to the bracket assembly with the cable or tape typically trained over three rollers so as to run in a reversible triangular loop. Rollers include two guide rollers at either end of the guiderail. Typically the upper roller is part of an upper roller assembly at the top of the guiderail and the lower roller is part of the lower roller assembly at the bottom of the guiderail. The third roller is a drive roller that is supported in a housing, and the drive roller is driven by an electric motor. The roller axis of the three rollers defines a triangle. The cable or flexible tape runs through the first conduit between the driver roller and the upper roller. Another portion of the cable or flexible tape runs in a second conduit that extends between the drive roller and the lower roller. The conduits are generally fixed to the upper roller, lower roller, drive roller, or a combination of them, with suitable base or bracket, and in the case of upper or lower rollers may also include a pin for attachment of the rollers. The conduits, bases or guiderail, or a combination thereof, may also be fixed to the inner door frame. Respective ends of the cable or flexible tape are attached to opposite sides of the bracket. Rotating the drive motor and drive pulley in a first direction of rotation will cause the bracket to move along the guiderail upwardly to the upper roller and associated stop. Reversing the direction of the drive motor and drive pulley will cause the bracket to slide along the guiderail in the opposite direction toward the lower roller and an associated bracket stop. The guiderails used in such regulator assemblies have frequently been stamped metal parts, and may be open on one or both ends, but frequently are closed on both ends, such that the closed ends provide an end stop for travel of the bracket as it is translated up and down in the channel.
Injection molding has also been proposed for use in the manufacture of guiderails; however, the necessary structural property of the guiderails generally dictates that injection molded parts be made from a filled plastic, including filled engineering plastic, such as a filled engineering thermoplastic. The filled plastics, such as those incorporating various strengthening particles or fibers are more difficult to feed into an injection molded part, and generally require higher pressures to fill the mold in a given configuration than the use of an unfilled plastic in the same mold configuration. The difficulty described coupled with the fact that the guiderails by their design are generally long thin-sectioned parts makes the design of suitable injection molds difficult for these parts. Still further, in addition to the guiderails having design requirements that require the use of filled plastics, it is also desirable to achieve a low co-efficient of sliding friction on the portion of the guiderail that acts as the rail and engages with the bracket that is translated within the channel or conduit formed in the rail. Generally, this has required the incorporation of low friction coefficient constituents, such as fluoropolymers, in the filled plastic, which are dispersed throughout the filled plastic in order to achieve a suitably low friction coefficient on the affected guiderail surfaces. The incorporation of constituents which provide the desired low coefficient of friction vary, since fluoropolymers and other low coefficient of friction constituents are generally expensive, and have a tendency to significantly increase the cost of such parts. Given the constraints described above related to the use of injection molding and the manufacture of window regulator guiderails, the use of injection molding to produce such parts has been quite limited.
Thus, there remains a need for improved polymer guiderails for various window regulator designs, as well as improved processes to enable their manufacture from various polymer materials.